The proposed investigation is designed to elucidate the effects of transplacental administration of N-ethyl-N-nitrosourea (ENU) on the postnatal development of rodent cerebellum and hippocampus. Since ENU-treated animals may develop tumors of the cerebellum and hippocampus, and tumorigenic incidence is highest during morphogenesis, this proposal hypothesizes that detectable developmental errors may be produced that might result in a predisposition to neuro-oncogenesis. A major emphasis will be placed on morphology, and several research methods (histology, histochemistry, electron microscopy) will be utilized; whenever possible, quantitative and stereologic analyses will be included. Autoradiographic studies of cell proliferation and differentiation, as well as the localization and fate of 14C-ENU, will also be conducted and correlated with structural observations. This research will delineate the teratogenic action of ENU, define the role of neurogenesis during chemical carcinogenesis, and explore the etiology and pathogenesis of brain tumors.